The train carriages have windows with ultra-violet filters to keep out the sun's glare, as well as carefully regulated oxygen levels with spare supplies to combat the thin air.

Zhu Zhensheng of the Chinese railway ministry called the new line a "major achievement" that will "hugely boost local development and benefit the local people".

But exiled Tibetan Lhadon Tethong said the railway was "engineered to destroy the very fabric of Tibetan identity".

"China plans to use the railway to transport Chinese migrants directly into the heart of Tibet in order to overwhelm the Tibetan population and tighten its stranglehold over our people," he said on a Free Tibet Campaign statement.

The Dalai Lama, Tibet's spiritual leader in exile since 1959, was more circumspect.

"The railway line itself is not a cause of concern for the Tibetan people," his spokesman, Thupten Samphel, said. "How it will be used is the main concern."